The long-term objective of this work is to identify molecular targets on the surface of enterotoxigenic E. coli (ETEC) that could be used in a vaccine. These organisms are globally the most common bacterial cause of serious diarrheal illness, perennially the most main infection associated with diarrhea in travelers, and an emerging cause of diarrheal illness in the US. Despite the relevance of these organisms to global human health, there is presently no broadly protective ETEC vaccine available. These studies will use newly available state-of the-art technology platforms designed specifically for this purpose. These will include both DNA (gene) and protein microarrays made available by the NIAID-sponsored Pathogen Functional Genomic Resource Center. Both the gene and protein microarrays encompass known or potential virulence factors from multiple ETEC strains making them extraordinarily useful tools for vaccine discovery. The aims of this project are: Aim 1. Indentify: (a). genes conserved among ETEC strains isolated from cases of severe cholera-like diarrheal illness, (b). virulence factors that are altered in response to infection. Both of sets of studies will use ETEC-specific DNA microarrays made available by the PFGRC. Aim 2. Indentify proteins that are recognized by antibodies following experimental infections in mice or natural infections in humans. These studies will use immuno-proteomic techniques including mass spectrometry and protein microarrays produced by the PFGRC. Aim 3. Finally, this project will test the protective efficacy of proteins identified as being both highly conserved (aim 1) and recognized during infection (aim 2) in a recently developed adult mouse model of ETEC infection. Following purification of the proteins, mice will be immunized and challenged with ETEC to test the ability of the candidate vaccine molecules to prevent infection.